Many useful applications rely on determining the distance that an object has moved. For example, it is useful to know the distance that a shipping container, a car, or even a valuable sculpture has moved. Another application for using the distance that an object has moved involved a computer mouse. Personal computers, such as desktop, laptop and notebook computers, typically include a computer mouse through which the user controls a cursor on a screen of the personal computer. The cursor moves across the screen based on the movement of the mouse.
One type of computer mouse includes a ball and a mechanism for detecting rotation of the ball as the user slides the mouse over a flat surface, such as a mouse pad. The mechanism includes two rollers that roll on the surface of the ball. Each roller is coupled to an emitter/detector that detects rotation and direction of rotation of the roller. One roller is used to detect movement in the x direction, and the other roller is used to detect movement in the y direction. The mouse also includes a processor that analyzes signals indicative of the detected movement. The user thereby moves the mouse to control the movement of an icon on the computer screen, such as a cursor.
A computer mouse that uses a ball has certain disadvantages. The ball does not roll if the working surface is not rough or sticky enough. Thus, mouse pads are typically used. Moreover, the ball picks up dirt and other unwanted particles as it rolls along the mouse pad. Dirt builds up on the rollers and degrades performance, such as when the cursor becomes stuck or moves only in one direction. In addition, the moving mechanical parts of the mouse are subject to wear and limit the life and utility of the mouse.
A second type of computer mouse addresses some of the aforementioned problems. Such an optical mouse has no ball and rollers and can become dirty. An optical mouse detects movement by reflecting light from the surface over which the mouse slides. Typically, light-emitting diodes (LEDs) are used to emit the light and detect the reflected light. But such LEDs and their associated electrical circuits are relatively expensive and complicated to manufacture. The optical mouse detects movement by detecting the reflection of light from a surface having a pattern. Therefore, an optical mouse may not accurately detect movement over a white piece of paper or even over an airplane tray table.
A computer mouse is sought that detects motion of the mouse using neither a ball nor light emitting diodes. Moreover, a computer mouse is sought that can detect the motion of the mouse moving over a surface that has no pattern.